Railway signaling



Aug. 9, 1938.

G. R. PFLASTERER RAILWAY S I GNALING Filed April 17. 1956 S-Shets-Sheet 2 INVENTOR Geopgafl. filase en HIS ATTORN EY 9, 1938. G. R. PFLASTERER 2,126,658 H RAILWAY S I GNALING Filed April'17, 1936 5 Sheets-Sheet 3 INVENTOR Geoige R. pfl aste en Q/ Km HIS ATTORNEY Patented Aug. 9, 1938 UNITED STATES PATENT OFFICE Application April 17, 1936, Serial No. 74,876

16 Claims.

My invention relates to railway signaling, and particularly to signaling involving wayside signals located along a trackway for governing the passage of trains.

A feature of my invention is the provision of novel and improved apparatus-for establishing a distinctive control for each of three track sections in the rear of an occupied section. Each distinctive control is effective to cause a corresponding aspect of the associated wayside signal, whereby there is produced a three-block, fourindication, system of signaling.

The present invention is an improvement on the apparatus disclosed and claimed in an application Serial No. 68,807 for Letters Patent of the United States, filed March 14, 1936, by Leslie R. Allison, for Railway signaling, and in my application Serial No. 68,497, filed March 12, 1936, for Railway signaling.

I will describe one form of apparatus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawings, Figs. 1A and 1B are diagrammatic views which, when placed end to end in the order named, illustrate one form of three-block, four-indication, signaling system embodying my invention. Fig. 2 is a diagrammatic view illustrating a modification of a portion of Fig. 1A and also embodying my inven- 30 tion.

Similar reference characters refer to, similar parts in each of the several views.

Referring first to Figs. 1A and 1B, the reference characters 1 and B designate the rails of a stretch :13 of railway track along which trafiic normally moves in the direction indicated by the arrows. The rails 'l and 8 are divided by insulated joints 9 into track sections W-X, X-Y, and Y-Z. As here shown, each track section is divided into two subsections, IT, 2T, 3T, 4T, etc.

Each subsection is provided with a track battery Ill connected across the rails at one end of the subsection and with a track relay, designated by the reference character TR' with a prefix the same as the numerical prefix of the associated subsection, connected across the rails at the other end of the subsection.

To govern the passage of trains through the stretch of railway, a wayside signal, designated by a suitable distinguishing reference character, is located at the entrance to each track section. 'As here shown, each signal is a color light signal comprising a green lamp G, a yellow lampY, and a red lamp R.

For controlling the signals, each section is provided with a direct current polarized signal control relay designated by the reference character I-ID with a prefix the same as the reference character 'of the associated signal.

Also for controlling the signals, each section is provided with a direct current relay 'of the well-known flasher type designated by the reference character F with a prefix the same as the reference character of the associated 'si'g'nal. Each flasher relay is provided with contacts which are normally biased to an initial de'energized position but which alternate between that position and a different position when the relay is energized. For example, relay IZF, when deenergihed, maintains its contact l5---=l'li constantly closed and its contact [l -48 constantly opened, but when the relay is energized, both contacts li -l6 and fl -I8 alternate periodically between their closed and opened condition.

The contacts of each relay F function in the same manner as described for the contacts of relay IZF.

Each section is provided with a pair of line conductors each of which extends through the section to the signal next in advance and each of which includes a front contact of each of the track relays of the associated subsections.

Each relay HD is connected directly to the associated pair of line conductors and each relay F is connected to the associated pair of line conductors through an asymmetric unit, a transformer, and a resistor designated by the reference characters Q, M, and E, respectively, each with a prefix the same as the reference character of the associated signal.

The relatively high impedance of the relays I-lD will prevent the flow of alternating current in these relays and the transformers M will prevent the energization of the relays F by direct current. The resistors F are provided to prevent excessive flow of direct current in the primary windings of the transformers M.

It will be seen, therefore, that the relays I-ID will respond to direct current only and the relays F will respond to alternating current only.

Each section is provided with a suitable source of direct current here shown as a battery 40 with its terminals designated by the reference characters B and C. V I

Each section is also provided with a transformer, designated by the reference character N with a prefix the same as the reference character of the associated signal, and having a primary winding l9 and a secondary winding 20. The secondary winding 20 of each transformer N is connected in series with the line circuit for the section next in rear so that when alternating current is supplied to the primary winding l9, alternating current will flow over the line circuit to control the relay F for the section next in rear.

For supplying alternating current to the primary winding IQ of the transformers N, each section is provided with a device, designated by the reference character A with a prefix the same as the reference character of the associated signal, for converting direct current into alternating current. As here shown, each device A is an alternator of the well-known tuned reed type. Referring to alternator |3A, for example, the reference character 2| designates a reed which is caused to vibrate between terminals 22 and 23 by a control winding 24. In the deenergized condition, reed 2| does not connect with either termi-' nal 22 or terminal 23 but does connect with the terminal 25. When energy is supplied to the alternator |3A, winding 24 will attract reed 2| causing it to connect with terminal 23 and to move away from terminal 25, causing winding 24 to become deenergized. Upon the deenergization of winding 24, the resilience of reed 2| will cause it to move away from terminal 23 and to connect with terminal 22 as well as with terminal 25. The circuit for winding 24 will then be completed so that reed 2| again will go through the cycle of operation justdescribed. Winding 24, therefore, will be repeatedly energized and deenergized as long as energy is supplied to its control circuit. When reed 2| connects with terminal 23, current is then supplied to. the right-hand portion of primary winding l9 of transformer |3N; and when reed 2| connects with terminal 22, current is then supplied in the opposite direction to the left-hand portion of primary winding l9. Alternating current, therefore, will be induced in the secondary winding 20 of transformer I3N whenever alter nator |3A is operating.

The alternator A for each of the other sections functions to supply alternating current to the associated transformer N in a manner identical to that described for alternator |3A.

Each section is provided with a pole changing relay having a slow releasing characteristic and designated by the reference character PC with a prefix the same as the reference character of the associated signal. As will be explained more in detail hereinafter, each relay PC is controlled by the associated relays HD and F in such a manner that the relays PC are energized whenever the associated relay HD is energized in the normal direction or whenever the'associated relay F is energized provided the associated relay HD also is energized. Whenever the relays PC are energized, the line conductors for the section next in rear of the associated section are supplied with direct current in the normal direction. Whenever the relays PC are deenergized, such line conductors in the rear are supplied with direct current in the reverse direction and also with alternating current provided the associated polarized relay HD is then energized in the reverse direction.

Each of the color light signals is controlled by the associated relays HD, F, and PC in the following manner When relay HD is deenergized (see jsignal l4) the red lamp R, of that signal is lighted Signal I4, therefore, is displaying a red light to indicate stop. When relay HD is energized in the reverse direction and relay F is deenergized (see signal I3), the yellow lamp Y of that signal is lighted by an uninterrupted circuit which passes from terminal B through front point of contact 28 of relay |3HD, reverse polar contact 2930 of relay |3HD, constantly closed contact 3|32 of relay |3F, and lamp Y to terminal C. Signal I3, therefore is displaying an uninterrupted yellow light to indicate prepare to stop lat next signal. When relay HD is energized in the reverse direction and relay F also is energized (see signal I2), the yellow lamp Y of that signal is lighted by an interrupted circuit which passes from terminal B through front point of contact 33 of relay |2HD, reverse polar contact 3425 of relay |2HD, intermittently closed contact |5|5 of relay |2F, and lamp Y to terminal C. Signal l2, therefore, is displaying an interrupted or flashing yellow light to indicate approach next signal at medium speed. When relay HD is energized in the normal direction (see signal II), the green lamp G of that signal is lighted by a circuit which passes from terminal B through front point of contact 36 of relay |IHD, normal polar contact 31-38 of relay HHD, and lamp G to terminal C. Signal therefore, is displaying a green light to indicate proceed at normal speed.

As here shown, a train K is indicated diagrammatically in the section immediately to the right of location Z so that relay |4HD is deenergized with the result that the relay |4PC also is deenergized.

Since relay |4PC is deenergized, relay |3HD is energized in the reverse direction over a circuit which passes from terminal B of battery 40 at signal l4, through back point of contact 4| of relay |4PC, secondary winding 20 of transformer |4N, front contact 42 of relay 6TB, front contact 43 of relay 5TH, relay |3HD, front contact 44 of relay 5TB, and front contact 45 of relay BTR, and back point of contact 46 of relay MPG to terminal C of battery 40.

When relay |3HD is energized in the reverse direction and relay |3F is deenergized, relay |3PC, of course, will remain deenergized. Since relay |3HD is energized in the reverse direction and relay |3PC is deenergized, the operation of alternator |3A is initiated by a circuit which passes from terminal B through front contact 41' of relay |3HD, reverse polar contact 4849 of relay |3HD, back contact 50 of relay |3PC, and alternator A to terminal C.

Since relay |3PC is deenergized and alternator |3A is operating, relay |2HD is energized in the reverse direction and relay |2F also is energized. The circuit for relay |2HD may be traced from terminal B of battery 40 at signal l3 through back point of contact 5| of relay |3PC, secondary winding 20 of transformer |3N, front contact 52 of relay 4TB, front contact 53 of relay 3TB, relay I2HD, front contact 54 of relay 3TR, front contact 55 of relay 4'I'R, and back point of contact 5B of relay |3PC to terminal 0. The circuit for relay I21 may be traced from one terminal of secondary winding 20 of transformer |3N through front contact 52 of relay 4TH, front contact 53 of relay 3TB, resistor |2E, transformer 2M, asymmetric unit |2Q, relay |2F, front contact 54 of relay 3TR, front contact 55 of relay 4TH, back point of contact 56 of relay |3PC, battery 40 at signal 3, and back point of contact 5| of relay |3PC to the other terminal of secondary 20 of transformer |3N.

Since both relays |2HD and I21 are energized,

relay l 2P0 is energized over a circuit which passes from terminal B through contactll 1-|8 of relay I2F, front contact BJ of relay IZHD, and relay lZPC'to terminal C. Although the contact l1- .l8 of relay 'lZ-F will be alternately closed and opened, the slow releasing characteristic of relay I 21C .will prevent this relay from dropping away during the open circuit periods.

Since relay IZPC is energized, relay llHD is energized in the normal direction over a circuit which passes from terminal 3' of battery 40 at signal 12 through front point of contact 58 of relay IZPC, front contact 59 of relay 2TB, front contact 60 of relay ITR, relay III-ID, front contact 6| of relay ITR, front contact 62 of relay 2TB, secondary winding 20 of transformer IZN, and front point of contact 63 of relay IZPC toterminal C.

'Since relay IIHD is energizedin the normal direction, relay HPC also is energized over a circuit 'whichpasses from terminal B through front contact 64 of relay IIHD, normal polar contact Bil-66 of relay HHD, and relay PC to terminal C. When relay IIBC is energized, the line circuit for the section next in rear of location W will be supplied with direct current in the normal direction so that the signal (not shown) controlled by such rear line circuit will be displaying the normal proceed indication.

Summing up then, it will be seen that when a section is occupied by a train, the signal for that section will display a red light to indicate stop, the signal for the section next in rear will display an uninterrupted yellow light to indicate approach next signal prepared to stop, the signal for the second section in rear will display a flashing yellow light to indicate approach next signal at medium speed, and the signal for the third section in rear will display a green light to indicate proceed at normal speed. The apparatus embodying my invention, therefore, provides four distinctive indications with the use'of the usual three unit color light signal.

The slow releasing characteristic of the relays PC will prevent tumble-down of the signal control circuits to the rear during pole changing periods. For example, when the train K passes out of the section to the right of location Z so that relay |2HD becomes energized in the normal direction to cause signal l2 to display the normal proceed indication, current will be momentarily disconnected from relay I2PC during the time this relay is being transferred from control by contact l'l-IB of relay [2F and front contact 51 of relay l2I-ID to control by front contact 69and normal polar contact 9 l- -92 of relay IZHD. During this period, however, front points of contacts 58 and 63 of relay IZPC will not become opened so that the energization of the line circuit for the section W-X will not be disturbed.

The control of the red lamp R by a back contact of the associated relay PC also prevents a momentary flash of the red lamp during pole changing periods. For example, back contact 61 of relay IZPC does not become closed during the pole changing period mentioned above even though back'point of contact 33 of relay l2I-ID does become momentarily closed. The red lamp R, therefore, cannot become lighted during the changes of polarity in the energization of theassociated control relay HD.

Referring now to Fig. 2, the reference character H designates a direct current polarized signal control relay having a retained neutral characteristic. The relay H is connected directly to the pair of line conductors in the same manner as described for the relay HD shown in Figs. 1A and 1B.

The reference character J designates a direct I current neutral relay which is connected to the line conductors by a resistor E, a transformer M, and an asymmetric unit Q in the same manner as described for the relay F shown in Figs. 1A and 18. The relay F is a flasher relay of the type employed in the system shown in Figs. 1A and 1B and is controlled by a front contact 10 of the relay J and, therefore, will be energized or deenergized according as the relay J is energized or deenergized.

' The signal and associated apparatus shown in Fig. 2, when connected in a system, will function to provide a three-block, four-indication, signaling in a manner similar to that described for the signals and associated apparatus shown in Figs. 1A and 13.

Since the relay H is provided with a retained neutral feature, the slow releasing pole changing relay PC is no longer required to insure against tumble-down of the signal control circuits to the rear during pole changing periods or to prevent a momentary flash of the red lamp during such periods.

The relays H and F control the signal lamps in the following manner: When the relay H is deenergized, the red lamp R. of the signal will be energized by a circuit which passes from terminal B through back point of contact ll of relay H and lamp R to terminal C so that the signal Will display a red light to indicate stop. When the relay H is energized in the reverse direction, and relay J is deenergized so that relay F also is deenergized, the yellow lamp Y will be energized by an uninterrupted circuit to cause the signal to display a steady yellow light to indicate .approa'ch next signal prepared to stop. This circuit may be traced from terminal B through front point of contact "H of relay H, reverse polar contact 12'|3 of relay H, constantly closed contact '|4,T5 of relay F, and lamp Y to terminal C. When the relay H is energized in the reverse direction, and relay J is energized so that relay E also is energized, yellow lamp Y will be energized by an interrupted circuit to cause the signal to display a flashing yellow light to indicate approach next signal at medium speed." This circuit may be. traced over the. same path as previously described for the yellow. lamp, the only difierence being that contact it-1.5 of relay F Will be alternately opening and closing Whereas, when the relay F is deenergized, contact 15 7-71 Will remain constantly closed. When relay H is energized in the normal direction as shown in the drawingsthe green lamp G is energized over a circuit which passes from terminal B through front point of contact ll of relay H, normal polar contact ll-16 of relay H, and lamp G to terminal 0 so that the signal is displaying a green light to indicate proceed a o ma spe d The relays, H and J control the current supplied to the line circuit for the. section next in rearin the following manner: When relay H- is denergized, the. line. conductora for the section next in rear will be supplied with direct current energy in the reverse direction over back points of contacts I1 and 18 0f relay H.

When relay is energized in the reverse direction' and relay 3- is deenergized, the operation of alternator A will be initiated and the line conductors for the section next in rear will be supplied with alternating current simultaneously with direct current in the reverse direction; The circuit for alternator A may be traced from terminal B through back contact 19 of relay J, front contact of relay H, reverse polar contact 8i82 of relay H, and alternator A to terminal C. The direct current for the line conductors in the rear will be supplied from battery 40 over a path including back points of contacts 83 and 84 of relay J, reverse polar contacts 8586 and 8?88 of relay H, and front points of contacts H and 18 of relay H, and alternating current will be supplied to such conductors over the same path from secondary winding 20 of transformer N.

When relay H is energized in the reverse direction and relay J also is energized, the line conductors for the section next in rear will be supplied with direct current in the normal direction over front points of contacts 83 and 84 of relay J, reverse polar contacts 8585 and 31-88 of relay H, and front points of contacts TI and T8 of relay H.

When relay H is energized in the normal direction, the line conductors for the section next in rear will be supplied with direct current in the normal direction over normal polar contacts 89-81 and 9085 of relay H, and front points of contacts TI and 18 of relay H.

From the foregoing description of the two modifications of apparatus embodying my invention, it will be apparent that I have provided a three-block, four-indication, system wherein only two line conductors are required from signal to signal and wherein the usual three-indication unit color light signal may be utilized without adding additional indication units. Furthermore, my system requires no source of commercial alternating current and is economical in current consumption since alternating current is converted from the usual source of direct current only when traffic conditions are such as to require the display of a flashing yellow light.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention,'what I claim is:

1. In combination, a section of railway track, a pair of line conductors for said section, means governed in accordance with trafiic conditions in advance of said section for supplying said pair of conductors with current of one character or with current of another character simultaneously with current of said one character or with current of still a different character, a sign-a1 for said section including a first lamp and a second lamp, and means receiving energy from said pair of conductors for governing said lamps whereby only the first lamp is energized steadily if said conductors are supplied with current of said one character or only the first lamp is energized periodically if said conductors are supplied with current of said other character simultaneously with current of said one character or only the second lamp is energized if said conductors are supplied with current of said different character.

2. In combination, a section of railway track, a pair of line conductors for said section, means governed in accordance with traffic conditions in advance of said section for supplying said conductorswith direct current only or with alternating current simultaneously with direct current, a signal for said section including a lamp, and means receiving energy from said conductors for governing said lamp whereby the lamp is energized steadily if direct current only is supplied to the conductors or is energized periodically if alternating current is supplied simultaneously with direct current to said conductors.

3. In combination, a section of railway track, a signal for said section including a first lamp and a secondlamp, a first signal control relay and a second signal control relay, means governed in accordance with trafiic conditions in advance of said section for energizing only said first relay in one direction or for energizing said second relay simultaneously with the energization of said first relay or for energizing only said first relay in the other direction, a circuit for said first lamp which becomes steadily energized when only said first relay is energized in said one direction but which becomes periodically energized when both said relays are energized, and a circuit for said second lamp which becomes energized only when said first relay is energized in said other direction.

4; In combination, a section of railway track, a signal for said section including a first lamp and a second lamp, a first signal control relay and a second signal control relay, means governed in accordance with traific conditions in advance of said section for energizing only said first relay in one direction or for energizing said second relay simultaneously with the energization of said first relay or for energizing only said first relay in the other direction, a flasher relay which becomes energized when said second relay is energized, a circuit for said first lamp which becomes steadily energized when only said first relay is energized in said one direction but which becomes periodically energized when both said first relay and said flasher relay are energized, and a circuit for said second lamp which becomes energized only when said first relay is energized in said other direction.

5. In combination, a section of railway track, a signal for said section including a first lamp and a second lamp, a signal control relay and a flasher relay, means governed in accordance with tlafl'ic conditions in advance of said section for energizing only said signal control relay in one direction or for energizing said flasher relay simultaneously with the energization of said signal control relay or for energizing only said signal control relay in the other direction, and means controlled by said two relays for governing said lamps whereby the first lamp is energized steadily if only said signal control relay is energized in said one direction or is energized periodically if both said relays are energized and said second lamp is energized if said signal control relay is energized in said other direction.

I 6. In combination, a section of railway track, a signal for said section including a first lamp and a second lamp, a signal control relay and a flasher relay, means governed in accordance with traffic conditions in advance of said section for energizing only said signal control relay in one direction or for energizing said flasher relay simultaneously with the energization of said signal control relay or for energizing only said signal control relay in the other direction, a circuit for said first lamp including contacts of both relays whereby the first lamp is energized steadily if only said signal control relay is energizedin said one dir'ection but is energized. periodically if both said relays are energized; and means for energizmg said se'cond lamp eiiective onlyif said signal contr'ol relay is" energized saidother direction. 7; In combination-,- asection ofrailway track, a polarized relay' for said section anda flasher re? lay fors'aid section, means for deenergizin'g both said relays when said section is occupied, means for energizing only said: polarized relay in the normaldirection or for energizing only'said po larized relay in the reverse direction or for energizing said flasher relay simultaneously with the energizatibn ofsaid polarized relay the re verse direcmom a signal m said'section includimg a redand a yellow as well as a g-re'englamp, a circuit for said redla'mp including a back con-- tact of said? polarized relay, a circuit for said; yer- 10w lamp including a frontcontact of said polarizedrelay and a reverse polar contact of said p'olarized'relay'as well as a contact of said fiasher relay, and a circuit for said green lamp including a front contact of said polarized relay and a normal polar contactof saidpolarized relay.

8. In combination, a section of railway track having a track circuit including a track relay, a pair of conductors for said section each including a contact of said track relay, a polarized direct current line relay connected to said pair of con ductors, a flasher line relay receiving energy from said conductors through an asymmetric unit, means governed in accordance with traffic conditions in advance of said section for supplying said conductors with only direct current of one polarity or with alternating current simultaneously with direct current of said one polarity or with only direct current of the other polarity, and a signal lamp for said section governed by said two line relays whereby said lamp is constantly energized when said line conductors are supplied only with direct current and is energized periodically when said line conductors are energized with alternating current simultaneously with direct current.

9. In combination, a section of railway track having a track circuit including a track relay, a pair of conductors for said section each including a contact of said track relay, a polarized direct current line relay connected to said pair of conductors, a direct current neutral relay, means including an asymmetric unit for connecting said neutral relay to said conductors, a flasher relay governed by said neutral relay, means governed in accordance with traffic conditions in advance of said section for supplying said conductors with only direct current of one polarity or with alternating current simultaneously with direct current of said one polarity or with only direct current of the other polarity, and a signal for said section governed by said polarized relay and by said flasher relay.

10. In combination, a forward section and a rear section of railway track, a signal for the forward section, a signal control relay and a flasher relay governed by traffic conditions in advance of said forward section for governing said signal, another relay governed by said two relays, and a signal control circuit for the rear section governed by said other relay.

11. In combination, a section of railway track, a pair of conductors for said section, means for selectively supplying said pair of conductors with currents of three different characters respectively in accordance with traflic conditions in advance of said section, a signal for said section including a flrst lanipand asec'orid lamp, and; means se- Iectively re risivejmsaid' three characters of urrent f0l llghtll'lgSQTCf fiIS G lanip' steadily or saidfirst 1arr1epenbma1 yor said second lamp whereby said signal is"ca1'1sejd to display three distinctive indications-to co'rrespondto said three characters of current;

1 21'A railway signaling]systzarn comprising a stretchof railway trackdividedjinto sections, a pairfoff jconductdr's for each sectio' *means for each sc'tio'nvfo r supplying: the associated pair of conductors with currents of three different charactersrespectively infaccordancewith traffic cond n's in advance ofsuch section, a signal for e h ecti'on,and means for each section'selectively'responsiveto said three characters of cur rent for controlling the" associated signal in such nher that sai dj signal is" caused" to display a steady light drone color or a flashing light of said one color or a l ight'of a difierent color'to correspond to saidth'ree characters of current respectively. H

l3, raj railway signalingi system comprising a' stretch of railway track divided into sections, a pair of conductors for each section governed by trafiic conditions in that section, means for each section for supplying the associated pair of conductors with currents of three different characters respectively in accordance with trafiic conditions in advance of such section, control means for each section capable of assuming one condition when the associated section is occupied and three other distinctive conditions to correspond to said three characters of current when the associated section is unoccupied, and a signal for each section governed by the associated control means in such a manner that said signal is caused to display a light of one color or a steady light of another color or a flashing light of said other color or a light of still a different color to correspond to the four conditions of said control means.

14. In combination, a stretch of railway track divided into a plurality of successive block sections each having a pair of conductors governed by traffic conditions in said section, a signal for each section comprising a plurality of lamps, a polarized direct current relay for each section energized from the conductors for such section and selectively controlling circuits through which current may be supplied to the lamps of the signal for such section, a control relay for each section energized from the conductors for such section, said control relay being responsive only to alternating current supplied to said conductors, means controlled by said control relay and operative only when said control relay is energized to periodically establish and interrupt the circuit for supplying current to at least one of the lamps of the signal for such section, the polarized relay associated with each block section controlling the supply of alternating current to the conductors of the adjacent block section in the rear, the polarized relay and the control relay for each block section jointly controlling the supply of direct current to the conductors of the adjacent block section in the rear.

15. In combination, a stretch of railway track divided into a plurality of successive block sections each having a pair of conductors governed by trailic conditions in said section, a signal for each section comprising a plurality of lamps, a polarized direct current relay for each section energized from the conductors for such section and selectively controlling circuits through which current may be supplied to the lamps of the signal for such section, a control relay for each section energized from the conductors for such section, said control relay being responsive only to alternating current supplied to said conductors, means controlled by said control relay and operative only when said control relay is energized to periodically establish and interrupt the circuit for supplying current to at least one of the lamps of the signal for such section, each block section having associated therewith an alternating current generator operative on the supply of direct current to supply alternating current to the conductors of the adjacent block section in the rear, the polarized relay associated with each block section controlling the supply of direct current to the alternating current generator for such block section, the polarized relay and the control relay for each block section jointly controlling the supply of direct current to the conductors of the adjacent block section in the rear.

16. In combination, a stretch of railway track divided into a plurality of successive block sections each having a pair of conductors governed by traffic conditions in said section, a signal for each section comprising a plurality of lamps, a polarized direct current relay for each section enerized from the conductors for such section and selectively controlling circuits through which current may be supplied to the lamps of the signal for such section, a control relay for each section energized from the conductors for such section, said control relay being responsive only to alternating current supplied to said conductors, the polarized relay associated with each block section controlling the supply of alternating current to the conductors of the adjacent block sec tion in the rear, the polarized relay and the control relay for each block section jointly contro1 ling the supply of direct current to the conductors of the adjacent block section in the rear, and means controlled by one of said relays for each block section for periodically establishing and interrupting a circuit through which current may be supplied to at least one of the lamps of the signal for such block section.

GEORGE R. PFLASTERER. 

